Members of the NDR (nuclear Dbf2-related) protein-kinase family are essential components of pathways that control important cellular processes, such as morphological changes, mitotic exit, cytokinesis, cell proliferation and apoptosis. Recent progress has shed light on the mechanisms that underlie the regulation and function of the NDR family members. Combined data from yeast, worms, flies, mice and human cells now highlight the conserved and important roles of the different NDR kinases in distinct cellular processes.

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Human NDR1 and 2 (NDR1/2) are serine-threonine protein kinases in a subgroup of the AGC kinase family. The mechanisms of physiological NDR1/2 activation and their function remain largely unknown. Here we report that Fas and TNF-alpha receptor stimulation activates human NDR1/2 by promoting phosphorylation at the hydrophobic motif (Thr444/442). Moreover, NDR1/2 are essential for Fas receptor-induced apoptosis as shown by the fact that NDR knockdown significantly reduced cell death whereas overexpression of the NDR1 kinase further potentiated apoptosis. Activation of NDR1/2 by death receptor stimulation is mediated by the tumor suppressor RASSF1A. Furthermore, RASSF1A-induced apoptosis largely depends on the presence of NDR1/2. Fas receptor stimulation promoted direct phosphorylation and activation of NDR1/2 by the mammalian STE20-like kinase 1 (MST1), a downstream effector of RASSF1A. Concurrently, the NDR1/2 coactivator MOB1 induced MST1-NDR-MOB1 complex formation, which is crucial for MST1-induced NDR1/2 phosphorylation upon induction of apoptosis. Our findings identify NDR1/2 as novel proapoptotic kinases and key members of the RASSF1A/MST1 signaling cascade.

Our observations propose a novel pathway in control of human centriole duplication after recruitment of HsSAS-6 to centrioles.

MOB proteins are integral components of signaling pathways controlling important cellular processes, such as mitotic exit, centrosome duplication, apoptosis, and cell proliferation in eukaryotes. The human MOB protein family consists of six distinct members (human MOB1A [hMOB1A], -1B, -2, -3A, -3B, and -3C), with hMOB1A/B the best studied due to their putative tumor-suppressive functions through the regulation of NDR/LATS kinases. The roles of the other MOB proteins are less well defined. Accordingly, we characterized all six human MOB proteins in the context of NDR/LATS binding and their abilities to activate NDR/LATS kinases. hMOB3A/B/C proteins neither bind nor activate any of the four human NDR/LATS kinases. We found that both hMOB2 and hMOB1A bound to the N-terminal region of NDR1. However, our data suggest that the binding modes differ significantly. Our work revealed that hMOB2 competes with hMOB1A for NDR binding. hMOB2, in contrast to hMOB1A/B, is bound to unphosphorylated NDR. Moreover, RNA interference (RNAi) depletion of hMOB2 resulted in increased NDR kinase activity. Consistent with these findings, hMOB2 overexpression interfered with the functional roles of NDR in death receptor signaling and centrosome overduplication. In summary, our data indicate that hMOB2 is a negative regulator of human NDR kinases in biochemical and biological settings.